A method of UE's location based AP clustering & beamforming for cell-free networks

Abstract

A Method of UE's Location Based AP Clustering & Beamforming for Cell-Free Networks The invention relates to a method of UE's location based AP clustering & beamforming for cell-free networks.

Description

[0001] A Method of UE’s Location Based AP Clustering & Beamforming for Cell-Free Networks

[0002] TECHNICAL FIELD

[0003] The invention relates to a method of UE’s location-based AP (Access Point) & beamforming for cell-free networks.

[0004] PRIOR ART

[0005] In the prior art, it is emphasized that location information of UE’s (User Equipment’s) is of critical importance in the field of telecommunications.

[0006] Cell-free mMIMO (CF mMIMO) is a novel technique that combines the benefits of ultra- dense networks with massive MIMO (mMIMO) technology to address their respective shortcomings in document [1], User Centric Cell-Free System is shown in document [1], The term was coined in document [2] and refers to a network with more APs than UEs. The APs collaborate to serve the UEs through joint transmission and reception. To picture this technique, we can assume a network with a single mMIMO array. Then this array can be taken apart and individual antennas can be placed at different places utilizing the same transmission / reception algorithms to realize the CF mMIMO concept as depicted in document [2], To serve a specific UE, scattered antennas transmit data signals with varying power and phase-shifts. This ensures synchronous delivery and increase in received signal power. Regarding the uplink part, signals from separated antennas are combined to retrieve data from each UE.

[0007] Regardless of how one approaches CF mMIMO technology, its primary characteristics are that it has a large number of geographically dispersed access points (APs) and that the coverage area is not separated into discrete cells. As shown in Figure 1 , every UE is served by every AP (Access Point) in the vicinity. mMIMO processing eliminates interference in ultra-dense networks, resulting in a network without cells. Using multiple scattered AP antennas instead of a handful with massive arrays reduces SNR (signal to noise ratio) variations, which restricts the efficacy of standard cellular mMIMO. The goal of CF mMIMO is to create a network infrastructure that can provide consistent data rates across a coverage area [2], This focuses on improving user-experienced data rates rather than average or peak rates, which are already high in current networks.

[0008] A CF mMIMO system can be considered as a user-centric network, as each UE only receives signals from nearby APs [1 , and references therein]. As shown in Fig. 1 , each UE is served by a distinct collection of adjacent APs. The solution uses a Cloud Radio Access Network (C-RAN) infrastructure to enable flexible cooperation among surrounding APs [3], In CF mMIMO, APs connect to edge-cloud processors, sometimes known as Central Processing Units (CPUs), via fronthaul connections [2], Backhaul connections can be fully wired (using optical fiber cables) or partially wireless (using fixed microwave links).

[0009] Regarding the UE-centric dynamic clustering, determining the appropriate serving AP set and generating the beamforming vector is a challenge. It requires the dynamic knowledge of the location and / or received signal strength of the UE. In 5G NR, Positioning Reference Signal (PRS) is defined to estimate the location of the AP [4], The PRS is a feature introduced in 5G networks to support positioning services. It is used by devices to measure the time of arrival (ToA) and angle of arrival (AoA), which are crucial for determining the device's location. The signal is used by UE to perform measurements for positioning. These measurements are then reported back to the network, which calculates the UE's position using trilateration or triangulation methods

[0011] .

[0010] There exist various patent documents and articles in the literature. Some of them are explained below.

[0011] Patent document ON 113613315B relates to selection process and indication method of access point cluster in large-scale MIMO system without cellular cell. The selected access point cluster contains at least one main access point (AP); including an update period indication and indication of selection criteria; while ensuring the flexibility of access point cluster selection, it reduces signaling overhead and enables the access point cluster serving the UE to be updated in a timely manner, thereby ensuring the reliability of data transmission. However, the proposed method does not consider using the location information of UE for clustering.

[0012] Another approach is described in patent document CN114978256A. This patent document relates to Cellular-free large-scale MIMO system, adjustment method and adjustment device. The system comprises a plurality of UE (User Equipment), a plurality of APs (Access Points) and main control equipment, in a centralized processing mode based on UE elements, UE is used for acquiring and selecting an AP with the best communication quality with the UE as a main AP according to communication quality parameters of the UE and each AP; according to the communication quality parameters, selecting a plurality of APs providing communication services for the APs as an AP cluster set. The proposed method does not consider using the location information of UE for clustering.

[0013] The document [6] relates to the performance of cell-free massive MIMO in Rician fading,” in Proc. Each UE (AP) selects the M<N dominant APs (UEs), corresponding to the APs (UEs) having M largest large scale fading coefficients. Here, the UE selects M out of N APs. In other words, N is the total number of APs and M is the number of selected APs. The proposed methods do not consider using the location information of UE for clustering.

[0014] The article document [7] relates to User Association in Scalable Cell-Free Massive MIMO Systems. The principle of the competition-based selection is that any AP gives priority to the limited number of UEs providing the best channel conditions. The proposed methods do not consider using the location information of UE for clustering.

[0015] The document [8] relates to a clustering scheme based on timing requirements in coordinated base-stations cooperative communications. A clustering method that considers the synchronization problem is proposed. In this scheme, the cluster is composed of the areas that assure that the TDOAs (Time Difference of Arrival) of the users’ signals at the cooperating BSs are less than the CP (Cyclic Prefix) period. The proposed method is a fixed clustering method. It is not user centric. It does not consider the location information of UE. The document [9] relates to a user-centric virtual cell method to cell-free massive MIMO, in which a finite number of access points serve each user. The UC strategy beats the conventional CF one when utilizing basic estimate schemes, according to the results, unless there is a tiny percentage of users that have poor channel conditions. The proposed methods do not consider using the location information of UE for clustering.

[0016] The document

[0010] introduces a framework for structured massive access in cell-free massive MIMO systems. It includes an initial access algorithm, a partial large-scale fading decoding (P-LSFD) approach, two pilot assignment schemes, and one fractional power management policy. In order to allow a large number of UEs to access the network and choose the suitable APs for service, a scalable method based on a competitive process is offered. The proposed methods do not consider using the location information of UE for clustering.

[0017] The main technical problem is that according to the cell-free network definition, it is assumed that the UE can connect to all APs in the network. However, since this approach is not scalable, it is difficult to implement in practice. There are some methods such as AP clustering, etc., to ensure scalability. However, performing AP clustering in an optimal and dynamic way is a separate problem in the prior art. Moreover, the beamforming process cannot be done optimally.

[0018] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0019] BRIEF DESCRIPTION OF THE INVENTION

[0020] The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field.

[0021] The present invention relates to communications technologies, and in particular, to a method for UE’s location-based AP (Access Point) clustering & beamforming method for cell-free networks. Thanks to the proposed invention, it is aimed to solve dynamic AP clustering and beamforming problems in the prior art.

[0022] The invention proposes a novel of Location Based Clustering & Beamforming. In order to construct an appropriate (condition: the closest AP cluster to the UE as a distance) clusterfora UE, location information is important. Utilizing PRS signal defined in 3GPP standard, ToA and AoA information can be provided. Using these information cluster formation and beamforming vector generation is possible.

[0023] According to the cell-free network definition, it is assumed that the UE can connect to all APs in the network. However, since this approach is not scalable, it is difficult to implement in practice. AP clustering method has been proposed to ensure scalability. Performing this clustering in an optimal and dynamic way is an important problem. In addition to clustering, beamforming also needs to be done optimally. Therefore, within the scope of the invention, it is aimed to solve dynamic AP clustering and beamforming problems.

[0024] A main object of the invention is providing a method that is to determine the most appropriate AP (the closest AP to the UE as a distance) set and beamforming vector to serve the UE by using the location information of the UE.

[0025] Other objects of the invention:

[0026] • After the UE is connected to the AP with the strongest signal (initial access is provided) and this AP is selected as the master AP, selection of an AP cluster using the location information reported by the UE using PRS signaling,

[0027] • Determination of the beamforming vector using the PRS signal sent to the UE and the AoA (Angle of Arrival) information received by the UE from different APs,

[0028] • After the UE is connected to an AP cluster, the AP cluster serving the UE is dynamically determined by using the channel information (CQI-Channel Quality Indicator) reported periodically by the UE,

[0029] • If the signal level received from one of the APs serving the UE, other than the master AP, falls below a certain threshold value, the new AP is selected using the PRS signal, • If the signal level received by the UE from the master AP falls below a certain threshold value, the cell reselection process is triggered at the UE to determine a new set of APs to serve the UE.

[0030] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a method for UE’s location-based AP (Access Point) clustering & beamforming for cell-free networks.

[0031] Advantages of the invention: Thanks to the invention, it is possible to;

[0032] • The use of the location information of the UE obtained by using the PRS signal within the scope of the invention and the angle information to the APs to dynamically determine the most suitable AP set and beamforming vector to serve the UE, respectively,

[0033] • Using C-RAN (Cloud Radio Access Network) architecture, the AP cluster that will serve the UE and the beamforming vector that will be used to transmit data to the UE are centrally determined using the information from all APs,

[0034] • Monitoring the signal level received from each AP through the CQIs transmitted by the UEs and redetermining the AP cluster, when necessary, in order to avoid service interruption of the UE.

[0035] A possible embodiment of the invention is characterized in that three different APs are at least two access points and one master access point for determining user equipment location.

[0036] Another possible embodiment of the invention is characterized in that;

[0037] • trilateration or triangulation methods are used for estimating location information.

[0038] • missing angle of arrival (AoA) information among the APs included in the cluster is used for forming cluster,

[0039] • signal used for tracking is pilot signal as Channel State Information-Reference Signal,

[0040] • tracking is performed by CPU, • Channel State Information-Reference Signal (CSI-RS) is sent by candidate APs to UE.

[0041] To achieve all the objectives mentioned above and that will emerge from the following detailed description, the present invention relates to a method of UE’s location-based AP (Access point) clustering & beamforming for cell-free networks.

[0042] The proposed UE’s location-based AP clustering & beamforming method for cell-free networks is dependent on the computer implemented method. In the first aspect, the embodiment of the present invention relates to a method of UE’s location based AP clustering & beamforming method for cell-free networks, which can be executed by an apparatus for wireless communication at a base station in a wireless communications system (the apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory), or a network device, or by a component of the network device (such as a processor, a chip, or a chip system, etc.), or can be implemented by all or logical modules or software implementations of some network device functions or computer implemented device.

[0043] User equipment (UE) is any device used directly by an end-user to communicate. It can be a hand-held telephone, mobile phone, smart devices, a laptop computer equipped with a mobile broadband adapter, or etc. It connects to the base station Node B / eNodeB.

[0044] Other aspects, features, and embodiments will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary aspects in conjunction with the accompanying figures. While features may be discussed relative to certain aspects and figures below, all aspects can include one or more of the advantageous features discussed herein. In other words, while one or more aspects may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various aspects discussed herein. Such exemplary aspects can be implemented in various devices, systems, and methods.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure, in accordance with one or more various examples, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict examples of the disclosure. These drawings are provided to facilitate the reader's understanding of the disclosure and should not be considered limiting the breadth, scope, or applicability of the disclosure. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.

[0046] Figure 1 : Proposed User Centric Cell-Free Network Architecture

[0047] REFERENCE NUMBERS GIVEN IN THE FIGURE

[0048] The reference numbers of the elements included in the figures are explained below.

[0049] 1 CPU

[0050] 2 Fronthaul

[0051] 10 AP1

[0052] 11 AP2

[0053] 12 AP3

[0054] 13 AP4

[0055] 20 UE1

[0056] 21 UE2

[0057] 22 UE3

[0058] 30 Cluster of UE1

[0059] 31 Cluster of UE2

[0060] 32 Cluster of UE3

[0061] DETAILED DESCRIPTION OF THE INVENTION

[0062] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only to make the subject more understandable. To achieve all the objectives mentioned above and that will emerge from the following detailed description.

[0063] The method of the invention is to determine the most appropriate (AP closest to the UE (user equipment) as a distance) AP cluster and beamforming vector to serve the UE by using the location information of the UE. Proposed User Centric Cell-Free Network Architecture which is including Central Processing Unit (CPU (1 )), fronthaul (2), access point 1 (AP1 (10)), access point 2 (AP2 (11 )), access point 3 (AP3 (12)), access point (AP4 (13)), user equipment 1 (UE1 (20)), user equipment (UE (21)), user equipment (UE (22)), user equipment (UE (23)), cluster of UE1 (30), cluster of UE1 (31) and Cluster of UE1 (32) are shown figure 1.

[0064] In order for the invention to be implemented that is sufficient to have at least two APs. One of these APs is the master AP and the user can first connect to that AP. As long as the signal received from the other AP is at a certain level (Channel Quality Indicator (CQI) at a 0-15 (as it is known in standards)), in this way, it is possible to receive service.

[0065] Master AP: Master AP is the access point (AP) where the user receives the strongest signal. Therefore, the UE connects to the network through this AP.

[0066] The main novelty and differences in the proposed method starts with selecting at least one the master access point (AP) and at least one the closest APs by CPU (1 ) to send Positioning Reference Signal (PRS) to the user equipment (UE) for estimating the user equipment’s location.

[0067] The proposed computer implemented method which is suitable for being used with a communication network which is a user-centric cell-free network where each access point (AP) is connected to the network is synchronized, wherein the communication network is comprising;

[0068] ■ At least one master access point in the coverage area,

[0069] ■ At least one access point which is the closest to the master access point in the coverage area,

[0070] ■ At least one user equipment (UE) which is connected to network,

[0071] ■ At least one Central Processing Unit (CPU (1 )) which is connected to the network, characterized in that the method ensures determining the closest access point (AP) cluster to the user equipment (UE) as a distance and beamforming vector to serve the UE by using the location information of the user equipment (UE) for UE’s location-based AP clustering & beamforming method for cell- free networks which is suitable for being used with a communication network, wherein the method is characterized by after performing the steps of;

[0072] • Listening Synchronization Signal Block (SSB) signal which is coming from the base stations by user equipment (UE) in the coverage area (Here, listening SSB signals connecting each UE to the network through a master AP, which is the AP that UE gets the strongest SSB (Synchronization Signal Block) signal (Here, strongest SSB signal means that before connecting to the network, the UE listens to the SSB signals coming from the base stations around it. It connects to the base station with the strongest of these signals. Apart from this, there is no strongest SSB signal requirement.),

[0073] • Connecting each user equipment (UE) to the network through a master access point (AP),

[0074] • After connecting the master access point, completing synchronization and random-access processes by providing the UE synchronizes to the base station in the downlink direction via SSB signalling,

[0075] • After the completion of synchronization in the downlink direction, completing synchronization by the user equipment (UE) in the uplink direction by using Random Access Channel (RACH) procedure (After the initial access (Initial access is the phase where the UE listens to the SSB signals from the base stations around it and connects to the strongest one), synchronization and random-access processes are completed (this completed process is provided by the UE synchronizes to the base station in the downlink direction via SSB signaling. After the completion of this synchronization in the downlink direction, the UE completes its synchronization in the uplink direction with the help of the RACH (Random Access Channel) procedure.)), comprising the steps of;

[0076] • Selecting at least one the master access point (AP) and at least one the closest APs by CPU (1) to send Positioning Reference Signal (PRS) to the user equipment (UE) for estimating the user equipment’s location, • Sending the Time of Arrival (ToA) and angle of arrival (AoA) information by UE to the network to which the user equipment is connected,

[0077] • According to the ToA information of three different APs (combining at least one master AP and at least two another APs), estimating the location of the UE by the CPU (1 ) (these methods can be as it is general known in literature such as trilateration or triangulation methods etc.),

[0078] • Using the estimated location information, forming of the cluster by the closest three APs including the master access point (AP) (Using the estimated location information (Here estimation process by doing: APs with the closest distance are selected from the UE-AP distances estimated via the PRS signal.), the cluster is formed (here formed process by doing: AP cluster is created from selected APs. The rendering condition is explained in the comments above. These selected APs only send data signals to the UE. Control signalling is done through the master AP) by the closest three APs including the master AP),

[0079] • If angle of arrival (AoA) information of any AP that belongs to the cluster is absent, then sending PRS by this AP to get the angle of arrival (AoA) information,

[0080] • Using the angle of arrival (AoA) information provided by the AP’s in the cluster (Using the AoA information (Here, using of information by; the angle information between the UE and the APs serving the UE is learned through AoA and this information is used to determine the beamforming vector) provided by the AP’s (AP that is missing AoA (angle of arrival) information among the APs included in the cluster.) in the cluster, the beamforming vectors are generated to send the data signal to the user equipment,),

[0081] • Generating the beamforming vectors to send the data signal to the user equipment,

[0082] • Tracking the signal provided by the AP’s to determine Channel Quality Indicator (Tracking the CSI-RS reports (Here, CSI-RS (Channel State Information-Reference Signal) is the pilot signal sent by the base station to the UE to obtain channel information, provided by the APs (APs transmit the channel information they obtain from the UEs connected to them to the CPU (1 ) via the CSI-RS signal. Tracking is done by the CPU (1).) to determine channel quality indicator (CQI)),

[0083] • If the channel quality indicator (CQI) of an AP other than master AP falls below a configurable threshold, then selecting a new access point (AP) by using the new estimated location information. If the channel quality (CQI (Channel Quality Indicator) is obtained by quantizing the received power measured in dBm by the UE via CSI-RS and converting CQI into a value between 0-15 (if the value goes to close 15, it is assumed that is good channel quality or if the value goes to close 0, it means that is low channel quality. There is possible to determine the threshold value, but the threshold value can be changed from operation / application to operation / application). This value is used to measure the channel quality.) of an AP other than master AP falls below a configurable threshold, then a new AP is selected using the new estimated location information (Here, when the signal level received by the UE from any of the APs it is connected to falls below a certain (determined) threshold value, the Positioning Reference Signal (PRS) is sent to the UE again by the candidate APs to select a new AP. Using the location information obtained through Positioning Reference Signal (PRS), the candidate AP closest to the UE is added to the AP cluster.),

[0084] • If the channel quality indicator (CQI) of the master access point (AP) falls below a configurable threshold, initiating a cell reselection process by user equipment, and forming a new cluster following the aforementioned step.

[0085] In the related method above, the difference and innovation of the invention starts after the RACH step.

[0086] The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention. References:

[0087] [1] Shuaifei Chen, Jiayi Zhang, Jing Zhang, Emil Bjdrnson, Bo Ai, “A survey on usercentric cell-free massive MIMO systems”, Digital Communications and Networks, Volume 8, Issue 5, 2022, Pages 695-719, ISSN 2352-8648, httDs: / / doi.org / 10.1016 / i.dcan.2021 .12.005.

[0088] [2] H.Q. Ngo, A. Ashikhmin, H. Yang, E.G. Larsson, T.L. Marzetta, Cell-free massive MIMO: uniformly great service for everyone, in: Proc, IEEE SPAWC, 2015, pp. 201- 205.

[0089] [3] C.M.R. Institute, C-RAN the Road towards Green RAN, White paper, Oct. 2011.

[0090] [4] 3GPP TS 38.211. "NR; Physical channels and modulation (Release 16)." 3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

[0091] [5] https: / / www. mathworks.com / helD / 5g / ug / nr-Drs-Dositioning.htm I.

[0092] [6] H. Q. Ngo, H. Tataria, M. Matthaiou, S. Jin, and E. G. Larsson, “On the performance of cell-free massive MIMO in ricean fading,” in Proc. IEEE ACSSC, 2018, pp. 980-984.

[0093] [7] C. D’Andrea and E. G. Larsson, "User Association in Scalable Cell-Free Massive MIMO Systems," 2020 54th Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, USA, 2020, pp. 826-830, doi: 10.1109 / I EEECONF51394.2020.9443536.

[0094] [8] A. M. Hamza and J. W. Mark, "A clustering scheme based on timing reguirements in coordinated base-stations cooperative communications," 2013 IEEE Wireless Communications and Networking Conference (WCNC), Shanghai, China, 2013, pp. 3764-3769.

[0095] [9] S. Buzzi and C. D’Andrea, "Cell-Free Massive MIMO: User-Centric Approach," in IEEE Wireless Communications Letters, vol. 6, no. 6, pp. 706-709, Dec. 2017, doi: 10.1109 / LWC.2017.2734893.

[0096]

[0010] S. Chen, J. Zhang, E. Bjdrnsson, J. Zhang, and B. Ai, “Structured massive access for scalable cell-free massive MIMO systems,” IEEE J. Sei. Areas Commun., vol. 39, no. 4, pp. 1086-1100, 2020.

[0097]

[0011] https: / / www. mathworks.com / helD / 5g / ug / nr-Drs-Dositioning.html

Claims

CLAIMS1. A computer implemented method which is suitable for being used with a communication network which is a user-centric cell-free network where each access point (AP) is connected to the network is synchronized, wherein the communication network is comprising;■ At least one master access point in the coverage area,■ At least one access point which is the closest to the master access point in the coverage area,■ At least one user equipment (UE) which is connected to network,■ At least one Central Processing Unit (CPU (1 )) which is connected to the network, characterized in that the method ensures determining the closest access point (AP) cluster to the user equipment (UE) as a distance and beamforming vector to serve the UE by using the location information of the user equipment (UE) for UE’s location-based AP clustering & beamforming method for cell- free networks which is suitable for being used with a communication network wherein the method is characterized by after performing the steps of;• Listening Synchronization Signal Block (SSB) signal which is coming from the base stations by user equipment (UE) in the coverage area,• Connecting each user equipment (UE) to the network through a master access point (AP),• After connecting the master access point, completing synchronization and random-access processes by providing the UE synchronizes to the base station in the downlink direction via SSB signalling,• After the completion of synchronization in the downlink direction, completing synchronization by the user equipment (UE) in the uplink direction by using Random Access Channel (RACH) procedure comprising the steps of;• Selecting at least one the master access point (AP) and at least one the closest APs by Central Processing Unit (CPU (1 )) to send a Positioning Reference Signal (PRS) signal to the UE for estimating the user equipment’s location,• Sending the Time of Arrival (ToA) and angle of arrival (AoA) information by UE to the network to which the user equipment is connected,• According to the ToA information of three different APs, estimating the location of the UE by the Central Processing Units (CPU (1 )),• Using the estimated location information, forming of the cluster by the closest three APs including the master access point (AP),• If angle of arrival (AoA) information of any access point (AP) that belongs to the cluster is absent, then sending a Positioning Reference Signal (PRS) by this AP to get the angle of arrival (AoA) information,• Using the angle of arrival (AoA) information provided by the access point (AP’s) in the cluster,• Generating the beamforming vectors to send the data signal to the user equipment,• Tracking the signal provided by the AP’s to determine Channel Quality Indicator,• If the channel quality indicator (CQI) of an AP other than master AP falls below a configurable threshold, then selecting a new access point (AP) by using the new estimated location information,• If the channel quality indicator (CQI) of the master access point (AP) falls below a configurable threshold, initiating a cell reselection process by user equipment, and forming a new cluster following the aforementioned step.

2. The method according to claim 1 , wherein said three different APs are at least two access points and one master access point for determining user equipment location.

3. The method according to claim 1 , trilateration or triangulation methods are used for estimating location information.

4. The method according to claim 1 , missing angle of arrival (AoA) information among the APs included in the cluster is used for forming cluster.

5. The method according to claim 1 , wherein said signal in tracking is pilot signal as Channel State Information-Reference Signal.

6. The method according to claim 1 , wherein said tracking is performed by Central Processing Units (CPU (1 )).

7. The method according to claim 1 , Channel State Information-Reference Signal (CSI-RS) is sent by candidate access points (APs) to user equipment (UE).

Images